4.6.1.4. EJB Local References

EJB 2.0 added local interfaces that do not use RMI call by value semantics. These interfaces use a call by reference semantic and therefore do not incur any RMI serialization overhead. An EJB local reference is a link in an application component naming environment that points to a deployed EJB local home interface. The name used by the application component is a logical link that isolates the component from the actual name of the EJB local home in the deployment environment. The J2EE specification recommends that all references to enterprise beans be organized in the java:comp/env/ejb context of the application component's environment.

An EJB local reference is declared using an ejb-local-ref element in the deployment descriptor. Each ejb-local-ref element describes the interface requirements that the referencing application component has for the referenced enterprise bean. The ejb-local-ref element contains the following child elements:

An optional description element that provides the purpose of the reference.
An ejb-ref-name element that specifies the name of the reference relative to the java:comp/env context. To place the reference under the recommended java:comp/env/ejb context, use an ejb/link-name form for the ejb-ref-name value.
An ejb-ref-type element that specifies the type of the EJB. This must be either Entity or Session.
A local-home element that gives the fully qualified class name of the EJB local home interface.
A local element that gives the fully qualified class name of the EJB local interface.
An ejb-link element that links the reference to another enterprise bean in the ejb-jar file or in the same J2EE application unit. The ejb-link value is the ejb-name of the referenced bean. If there are multiple enterprise beans with the same ejb-name, the value uses the path name specifying the location of the ejb-jar file that contains the referenced component. The path name is relative to the referencing ejb-jar file. The Application Assembler appends the ejb-name of the referenced bean to the path name separated by #. This allows multiple beans with the same name to be uniquely identified. An ejb-link element must be specified in JBoss to match the local reference to the corresponding EJB.

An EJB local reference is scoped to the application component whose declaration contains the ejb-local-ref element. This means that the EJB local reference is not accessible from other application components at runtime, and that other application components may define ejb-local-ref elements with the same ejb-ref-name without causing a name conflict. Example 4.10, “An example ejb-jar.xml ejb-local-ref descriptor fragment” provides an ejb-jar.xml fragment that illustrates the use of the ejb-local-ref element. A code sample that illustrates accessing the ProbeLocalHome reference declared in Example 4.10, “An example ejb-jar.xml ejb-local-ref descriptor fragment” is given in Example 4.11, “ENC ejb-local-ref access code fragment”.

    <!-- ... -->
    <session>
        <ejb-name>Probe</ejb-name>
        <home>org.jboss.test.perf.interfaces.ProbeHome</home>
        <remote>org.jboss.test.perf.interfaces.Probe</remote>
        <local-home>org.jboss.test.perf.interfaces.ProbeLocalHome</local-home>
        <local>org.jboss.test.perf.interfaces.ProbeLocal</local>
        <ejb-class>org.jboss.test.perf.ejb.ProbeBean</ejb-class>
        <session-type>Stateless</session-type>
        <transaction-type>Bean</transaction-type>
    </session>
    <session>
        <ejb-name>PerfTestSession</ejb-name>
        <home>org.jboss.test.perf.interfaces.PerfTestSessionHome</home>
        <remote>org.jboss.test.perf.interfaces.PerfTestSession</remote>
        <ejb-class>org.jboss.test.perf.ejb.PerfTestSessionBean</ejb-class>
        <session-type>Stateless</session-type>
        <transaction-type>Container</transaction-type>
        <ejb-ref>
            <ejb-ref-name>ejb/ProbeHome</ejb-ref-name>
            <ejb-ref-type>Session</ejb-ref-type>
            <home>org.jboss.test.perf.interfaces.SessionHome</home>
            <remote>org.jboss.test.perf.interfaces.Session</remote>
            <ejb-link>Probe</ejb-link>
        </ejb-ref>
        <ejb-local-ref>
            <ejb-ref-name>ejb/ProbeLocalHome</ejb-ref-name>
            <ejb-ref-type>Session</ejb-ref-type>
            <local-home>org.jboss.test.perf.interfaces.ProbeLocalHome</local-home>
            <local>org.jboss.test.perf.interfaces.ProbeLocal</local>
            <ejb-link>Probe</ejb-link>
        </ejb-local-ref>
    </session>
    <!-- ... -->

Example 4.10. An example ejb-jar.xml ejb-local-ref descriptor fragment

InitialContext iniCtx = new InitialContext();
Context ejbCtx = (Context) iniCtx.lookup("java:comp/env/ejb");
ProbeLocalHome home = (ProbeLocalHome) ejbCtx.lookup("ProbeLocalHome");

Example 4.11. ENC ejb-local-ref access code fragment